This invention relates generally to a circuit arrangement for detecting errors in print control apparatus for a printer, such as an impact line printer.
In printers of the type arranged to print characters or the like on a print sheet by impacting type characters carried on a type band or the like, by print hammers, the print hammers are driven at appropriate timing so that desired characters are printed. To this end, the contents of a character code memory, in which codes of type characters carried by a type band or the like are prestored, are compared with the contents of a print data memory in which codes of characters to be printed on a single print line are stored. When output data read out from the character code memory and/or from the the print data memory becomes abnormal, printing of correct characters cannot be attained. Therefore, in conventional circuit arrangements, parity checking is effected against the output data from these memories for determining whether the output data is normal or not.
However, this conventional technique for checking errors does not necessarily provide accurate checking or detection because parity check error is not resulted when malfunctions occurs in circuits which designate the address of the above-mentioned memories. Therefore, in the case that malfuncion occurs in such address-designating circuits, error printing cannot be detected while printing. As a result, printed characters had to be reviewed visually by human eyes.